sim: Enable logging in simulator test cases

When running simulations as unit tests, use a workaround from
https://stackoverflow.com/questions/30177845/how-to-initialize-the-logger-for-integration-tests
to initialize the logging system.

Signed-off-by: David Brown <david.brown@linaro.org>
diff --git a/sim/tests/core.rs b/sim/tests/core.rs
index dea9cfe..010f240 100644
--- a/sim/tests/core.rs
+++ b/sim/tests/core.rs
@@ -5,9 +5,12 @@
 extern crate bootsim;
 
 use bootsim::{ALL_DEVICES, RunStatus};
+use bootsim::testlog;
 
 #[test]
 fn core_tests() {
+    testlog::setup();
+
     let mut status = RunStatus::new();
 
     for &dev in ALL_DEVICES {